OK, what is this 8" rear I have?

OK, so I purchase this newly-built 3.25 pumpkin from an eBay store. (Yes, just another eBay story!) It was billed as: "8-Inch Ford Posi HD 4 pinion rear end". Installed about 3000 miles ago, but now this rear end behaves more like an open rear than a locking rear. ie: it'll leave marks from both tires for about 3 feet, then all power is transferred and the thing burns the passenger side tire like an open rear. Now that I know a bit more about what I'm looking at, I notice there is no counter-bore where the ring gear attaches to the diff. The housing is a waffle casting, so that appears correct. The guy says to send it back and he'll adjust it so it operates correctly. Whatdya think; did I get ripped-off for $575? GT1966

here's a couple pics:

....thought so.

Yeah, I started talking with a couple rear end guys at Carlisle at this past summer's Ford Nationals, describing my symptoms. Once I mentioned the company I did business with, both rear end guys said "You got ripped off"! Ugh. Yep, they knew of this eBay builder. I will first see how this gets resolved before I post a warning to others. Thanks for your insight. BTW, I could not find the eBay link to the other builder you sited in your reply.
Cliff